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Euxinia as a dominant process during OAEla(Early Aptian)on the Eastern Russian Platform and during OAElb(Early Albian)in the Middle Caspian

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Science China Earth Sciences 2017年第1期60卷 58-70页

作者： Svetlana O. ZORINA Oksana V. PAVLOVA Bulat M. GALIULL1N Vladimir P. MOROZOV Alexey A. ESKIN Institute of Geology and Petroleum Technologies Kazan Federal University 4/5 Kremlyovskaya street Kazan 420008 Russian Federation

A detailed study of the mineral composition and microstructure of the black shales associated with OAE1 a （Eastern Russian Platform）, OAElb （Middle Caspian）, and the host rocks has been carried out using X-ray diffraction, scanning electron microscopic, and microprobe analyses. The results provide important constraints for depositional environments in the sedimentary basins. Black shales with pyrite framboids imply euxinic （sulfidic） conditions with increased organic matter preservation. Disintegrating framboids suggest partial or complete dissolution of the organic matter inside the framboids due to increasing water oxygenation. OAEla on the Eastern Russian Platform is heterogeneous as it includes thin interbeds of concretionary coccolith limestones within the interval of bituminous shales, and correlates with the Lower Aptian Rhagodiscus angustus nannofossil zone. The coccolith limestones indicate short intermittent episodes of interrupted stagnation, rapid oxygenation, and restoration of normal marine conditions. The presence of montmorillonite, albite, microcline, and diopside in the bituminous siltstones and in the host siltstones of OAEla on the Eastern Russian Platform, as well as a high content of titanium in the black siltstones correlated with OAEIb in the Middle Caspian allow proposing significant input of pyroclastic material into the extant sea.

关键词： OAEIa OAElb Black shales pyrite framboids Euxinia Oxygenation Eastem Russian Platform MiddleCaspian Cretaceous

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Sedimentary Expressions of the Early Jurassic Jenkyns Event in an Inland Lacustrine System in the Yin'gen-Ejinaqi Basin,North China

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Acta Geologica Sinica(English Edition) 2024年第5期98卷 1359-1375页

作者： YANG Bing XU Guozhen HUI Guangji WEI Yi ZHANG Xinzhi YI Jinjun SUN Siyuan ZHANG Sujiang Cores and Samples Center of Natural Resources LangfangHebei 065201China Nanjing Institute of Geology and Palaeontology Chinese Academy of SciencesNanjing 210008China North China Institute of Science and Technology LangfangHebei 065201China

The Jenkyns Event,more widely known as the Toarcian Oceanic Anoxic Event(T-OAE),is marked by globally distributed negative carbon-isotope excursions,widespread oxygen depletion,and large-scale organic carbon burial,which indicate major climate/environmental perturbations in Earth's surface systems during the Early *** extensive research has been conducted in European continental settings,particularly in the western peri-Tethys regions,the impacts of this event beyond Europe remains largely ***,a multiapproach study including investigations into the sporepollen assemblages,pyrite framboids,clay minerals,total organic carbon(TOC)levels,and organic carbon isotope(δ13Corg)levels in a lacustrine borehole section(MED1)from the Yin'gen-Ejinaqi Basin,North China,provides evidence of the occurrence of the Jenkyns Event and its extensive sedimentary responses in the eastern Tethys terrestrial *** distinct spore-pollen assemblages have been identified in MED1(drilling depth:982.4 m to 1267.5 m),with the Cycadopites-Protopinus-Osmundacidites assemblage in the lower part(1267.5 m to 1132.9 m)indicating a middle Early Jurassic age and the Classopollis assemblage in the upper part(1132.9 m to 985.7 m)suggesting a Toarcian *** pyrite data suggest more anoxic conditions during the deposition of black mudstone and shale intercalations in the lower part of the Classopollis assemblage(1132.9 m to 1066.9 m),which combined with organic carbon enrichment and negativeδ13Corg excursions,are considered the paleoenvironmental response to the Jenkyns Event in the study ***,the evolution of vegetation groups changed from plant groups characterized by bisaccate and cycad pollen,as well as fern spores,to vegetation groups represented by Cheirolepidiaceae pollen across the Jenkyns Event,as evidenced by sporepollen data,together with the clay mineral assemblage change characterized by a notable increase in illite at the expense of kaolinite,

关键词： spore-pollen assemblages clay minerals pyrite framboids organic carbon isotope Jenkyns event

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